1. Field of the Invention
The present invention relates to an internal-combustion engine control method and to an engine using such a method.
2. Description of the Prior Art
There are known engines wherein opening/closing of the intake valve(s) is controlled by variable-timing control means. In this type of timing, the conventional camshaft is replaced by an actuating means dedicated to each valve, such as an electromagnetic or hydraulic or electrohydraulic or pneumatic or electropneumatic actuator, which acts directly or indirectly upon the valve rod. This allows changing the opening angles and times of the intake valves, as well as their lift laws or their opening frequency, while allowing multi-opening during a single running cycle of this engine. On the other hand, opening/closing of the exhaust valve(s) is controlled by any conventional timing means, such as a camshaft driven in rotation by a belt (or a timing chain) connected to the engine crankshaft. This engine type with two timing architectures is more commonly known as “half camless”.
Similarly, there are engines known as “full camless” that comprise no camshaft, whether for the intake valves or for the exhaust valves. In this case, the engine comprises an actuating means dedicated to each valve, such as an electromagnetic or hydraulic or electrohydraulic or pneumatic or electropneumatic actuator, which acts directly or indirectly upon the valve rod of the intake and exhaust valves.
In both engine types it is possible for example to have, for low and medium loads, a specific combustion such as a combustion with controlled auto-ignition (CAI) or a combustion with homogeneous charge compression ignition (HCCI) through phasing of the intake and exhaust valves allowing opening/closing of these valves with re-introduction or retention of burnt gases in the combustion chamber, as described in French Patent 2,760,487 filed by the assignee on combustion with controlled auto-ignition.
In the case of a half camless engine, considering that the exhaust valves are controlled by a camshaft, it is difficult to obtain such a combustion over a significant engine running range because the lift laws of these exhaust valves are difficult to modify during operation or they can only be modified over a very limited range.
For a full camless engine, the aforementioned drawback can be solved but to the detriment of an excessive production cost for this engine with installation of an actuator for each intake and exhaust valve, associated with a very sophisticated control of these actuators.
Furthermore, in the case of high engine loads, actuating the exhaust valves is difficult considering the stresses imposed by the high back pressures at the exhaust.
The present invention aims to overcome the aforementioned drawbacks by means of a method allowing a half camless engine to run like a full camless engine for low and medium loads.